“It is said the warrior’s is the twofold Way of pen and sword, and he should have a taste for both Ways.” ― Miyamoto Musashi, A Book of Five Rings: The Classic Guide to Strategy
I read…a lot. I read for a variety of reasons, but I always read material that teaches me something (or attempts to). With the advent of technology the access to good resources that are Martial Arts related has improved exponentially. You can Google MA books and resources and read the reviews of others who have read them and respectively approved or disapproved.
The key, though, is keeping the direct link between your study of Karate and your doing Karate. Karate, like many other Martial Arts is indeed a mental realm, but you can read, study, ponder and analyze all the material available to you by all the great writers, and still never become adept. On the other hand, if you study the written (and visual material) in conjunction with training in the Dojo you should see excellent progress.
Part of making karate your own is finding a balance. For example, I watch Iian Abernethy videos on Bunkai and I find that doing my Kata feels better and makes more sense. I read Shunryu Suzuki’s books such as Zen Mind, Beginner’s Mind and I can keep better focus for longer periods of training time.
What is written by the Pen that Musashi refers to above is the fodder for growth; the Sword on the other hand is that growth coming to life.
In my humble opinion: Reading Informs. Sweat Fortifies.